Various types of networks involving switches are in common use such as public and private telephone networks, local area networks (LAN) and wide area networks (WAN). LAN and WAN networks are digital and generally use asynchronous transfer mode (ATM) signals whereas telephone networks typically use analogue or synchronous digital signals (SONET). In ATM systems, the transmitted signals themselves carry the information that defines the destination of its payload. Similarly, in telephone systems, either analogue multitone signals define the number being called which is used to set up the connection or, for digital lines, coded frames of data are transmitted synchronously to define the desired connection. In other networks, such as token ring systems, data is passed around sequentially from one station to the next until the header information in that cell is recognized. In telephone networks, a host of central offices control communications with groups of subscribers either on analog lines or digital lines. Transmissions can take place between subscribers under the control of the same central office or between subscribers controlled by different central offices.
Broadband telecommunications networks involve networks containing hardware switches of various types and, for a given type, of various manufacturers. Such a network could contain frame, ATM and/or baseband analogue switches. For example, the switches in one city could be primarily analogue switches while those in another city could contain ATM switches or a mixture of ATM and analogue switches. In addition, the ATM switches could be made by various manufacturers as could the analogue switches. In general switches of one manufacturer are controlled differently by different protocols from those of other manufacturers and, in addition, could be configured differently. In order to set up a call the switch controller would have to know the protocol for each of the different switches involved. Moreover, if a given switch were changed to a switch of a different manufacturer, the protocol for that switch and its configuration, i.e. by a serial port or parallel ports, would have to be changed. Obviously, such a system is complex and inefficient.
In order for a call from one location to be connected to another location the system must be able to control each different make and type of switch in the path.
Obviously, there is a need for a simpler, switch independent method of setting up such a call.